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Petroleum Refinery Wastewater Treatment: Oil Removal, Phenolics, Sulfide, BOD Removal and Reuse

Petroleum refining is one of the most complex industrial wastewater generators. A modern refinery processes 100,000–500,000 barrels per day and generates 0.5–2.0 m³ of wastewater per tonne of crude processed. The wastewater carries the chemistry of petroleum refining: free and emulsified oil, phenols, sulfides, ammonia, cyanide, BOD from tank bottoms and process water, and trace heavy metals from catalysts. The combination of high organic load, toxic compounds, and the need for continuous high-reliability operation makes refinery wastewater treatment a specialized discipline. This guide covers the characterization and treatment train for crude oil refinery wastewater.

Refinery wastewater characteristics

Slaughterhouse Wastewater Treatment covers DAF (dissolved air flotation) technology that is foundational to refinery wastewater treatment, though the pollutant profiles differ significantly:

• Process water and tank draw-offs: Oil content 200–5,000 mg/L, phenols 50–500 mg/L, sulfides 5–100 mg/L, cyanide 1–20 mg/L, BOD 500–3,000 mg/L, COD 1,000–5,000 mg/L

• Desalter wastewater: Salt water from crude oil desalting (NaCl, MgCl₂, CaCl₂ 1,000–10,000 mg/L), oil 50–500 mg/L

• Sour water stripper effluent: High ammonia (500–2,000 mg/L), H₂S (50–500 mg/L), requires dedicated stripping

• Cooling tower blowdown: High dissolved solids, residual biocides and scale inhibitors

• Ballast and tank wash water: Variable, often high oil and solids

Total nitrogen 100–500 mg/L (dominated by ammonia), total phosphorus 10–50 mg/L, pH 6–10 depending on process unit.

Primary treatment: oil-water separation

Oil removal is the first priority. The API (American Petroleum Institute) separator is the traditional workhorse for refinery wastewater:

• Designed per API 421: gravity separation of free oil droplets above 150 microns

• Surface loading 10–20 m³/m²·day; retention time 30–60 minutes

• Removes free oil to 50–100 mg/L; emulsified oil passes through

• Must be heated above 10°C to keep waxes and heavy oils fluid

For tighter oil removal before biological treatment, Dairy Processing Wastewater Treatment DAF technology is applied to refinery wastewater: induced air flotation with chemical coagulation (ferric chloride 20–50 mg/L, polymer 2–5 mg/L) removes emulsified oil to below 20 mg/L and reduces BOD by 30–50%.

Phenolics and sulfide removal

Phenols (50–500 mg/L) and sulfides (5–100 mg/L) are toxic to biological treatment and must be removed in pre-treatment:

• Steam stripping: Sour water stripper (SWS) removes H₂S to below 10 mg/L and ammonia to below 50 mg/L using reflux steam. Standard refinery unit; the stripped H₂S goes to the sulfur recovery unit

• Solvent extraction for phenols: Phenols are extracted with light aromatic solvents (gasoline cut) in counter-current extractors, recovering phenols for sale. Reduces phenols by 80–95%

• Wet air oxidation: For high-concentration phenol streams (above 5,000 mg/L), wet air oxidation at 150–200°C converts phenols to biodegradable intermediates. Used for cresylic acid and tar decanter wastewater

Biological treatment

After oil removal and phenolics/sulfide stripping, refinery wastewater has BOD 200–1,000 mg/L suitable for biological treatment. Beverage Production Wastewater Treatment SBR technology is widely used in refinery wastewater treatment because of its robustness and operational flexibility:

• Sequencing Batch Reactor (SBR): Handles variable loads well; each batch can be monitored before discharge. Nitrification/denitrification is standard. BOD removal 90–95%; ammonia removal 80–95%

• Activated sludge with selector: Anoxic selector ahead of aeration tank controls filamentous sludge bulking common in refinery wastewater. BOD removal 85–92%

• MBBR: Robust against toxic shocks from refinery process upsets. BOD removal 80–90%

Polishing and water reuse

Refinery wastewater after biological treatment (BOD below 20 mg/L, ammonia below 10 mg/L, oil below 5 mg/L) can be polished for reuse:

• Multimedia filtration: Removes residual suspended solids and oil to below 1 mg/L. Seawater Desalination Pretreatment media filtration specifications are directly applicable

• Activated carbon adsorption: Removes residual organics, phenols and color for boiler feed or cooling tower makeup

• RO for high-purity reuse: UF + RO achieves 70–80% recovery; RO product water suitable for demineralized water applications

Cost benchmarks

Frequently Asked Questions

Can refinery wastewater be discharged to sea?

Yes, many coastal refineries discharge to sea after treatment. Oil content must be below 10–15 mg/L, and many jurisdictions require BOD below 30–50 mg/L. Submarine outfalls provide dilution; the treated effluent must not cause visible oil sheen or harm marine life in the immediate vicinity.

What causes foaming in refinery wastewater aeration tanks?

Refinery wastewater aeration tanks are prone to stable foaming from residual surfactants, oily compounds and non-degradable polymers in the biological sludge. Control measures: antifoam dosing, hydraulic shear (spray headers), selector zones, and ensuring adequate sludge wasting to prevent sludge age buildup.

How do refineries handle contaminated stormwater?

Stormwater from paved areas is routed to the oily water sewer system and treated with refinery wastewater. Clean stormwater from uncontaminated areas (rooftops, clean yards) is kept separate and discharged directly or to stormwater drains. Oil-water separators at drain outlets catch initial stormwater flush (first flush), which carries the highest oil load.

Summary

Refinery wastewater treatment follows a well-established train: API separator, DAF for emulsified oil, sour water stripping for H₂S and ammonia, biological treatment (SBR preferred) for BOD and nitrogen, and multimedia filtration or carbon for polishing. Water reuse—particularly for cooling tower makeup and boiler feed—is a major driver for treatment investment. Industrial Water Pretreatment design for refinery reuse must address residual oil and sulfide that can foul or corrode downstream equipment.

Baihuipu Engineering supplies refinery wastewater treatment plants, API separators, DAF systems and sour water strippers to petroleum refineries globally.